Younger, More Affluent New Residents Are Reshaping the Vote in Metropolitan Regions of Denver, Atlanta, Washington, D.C.

LEESBURG, Va.—This was a pastoral, conservative Washington suburb until a decade ago, when new jobs sprouting in and around the U.S. capital began drawing younger, more affluent people like Bill and Heather King.

Mr. King, a traffic engineer, and Dr. King, a hospital pediatrician, sought to live among other young professionals in a place with the vibrancy of their urban hometowns—qualities they say they found in this former colonial...